How the Brain Works The Facts Visually Explained by DK (z-lib.org)

THE PHYSICAL BRAIN

Nerve Signals

FLUID INSIDE AXON

Direction of nerve

impulse

Nerve Signals

The brain and nervous system work by sending

signals through cells as pulses of electrical

charge and between cells either by using

chemical messengers called neurotransmitters

or by electric charge.

Action potential

Neurons signal by creating an action potential—a surge of

electricity created by sodium and potassium ions crossing

the cell’s membrane. It travels down the axon and

stimulates receptors on dendrites of neighboring cells.

The junction between cells is called a synapse. In many

neurons, the charge is carried over a minute gap between

axon and dendrite by chemicals, called neurotransmitters,

released from the tip of the axon. These junctions are

known as chemical synapses. The signal may cause the

neighboring neuron to fire, or it may stop it from firing.

Membrane channels

open to let ions in

HOW DOES A

NERVE COMMUNICATE

DIFFERENT INFORMATION?

Receiving cells have different

types of receptors, which respond

to different neurotransmitters.

The “message” differs according

to which neurotransmitters

are sent and received and

in what quantities.

Depolarization

Chemical changes from the cell body

allow positive ions to flood into the cell

through the membrane. That reverses the

polarization of the axon, making the

potential difference +30 millivolts.

Resting potential

When the neuron is at rest, there are more positive

ions outside the membrane than inside. This causes a

difference in polarization, or electrical potential, across

the membrane called the resting potential. The difference

is about –70 millivolts, meaning the outside is positive.

SOME NERVE IMPULSES

TRAVEL FASTER THAN

330 F T (100 M) PER

SECOND

CELL’S AXON MEMBRANE

Excess of ions inside

produces a positive charge

Excess of positive ions on

outside of cell membrane

KEY

Direction of

nerve impulse

Flow of ions

Positive ions

rush in

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US_022-023_Nerve_signals.indd 22 20/09/2019 12:31